Rif Eruvin 4b {Eruvin 15a continues ... 16b}

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4b

{Eruvin 15a continues}
{If the breach exactly equalled the standing:}
Rav Papa said: It is permitted.
Rav Huna the son of of Rav Yehoshua said: It is forbidden.
Rav Papa said: So did the All-Merciful teach Moshe: You should not have a majority breach.
Rav Huna the son of of Rav Yehoshua said: So did the All-Merciful teach Moshe: Fence the majority.

{Eruvin 16b}
And the halacha is like Rav Papa, for the Mishna may be analyzed in his way - "provided that the breaches are not more than the built-up portion" - implying that if they are equal, it is permitted.

Mishna:
A fence may also be constructed with three ropes, one above the other; providing the space between each rope be less than three handbreadths, and the measure {=thickness} of the three ropes together exceed one handbreadth, so that the entire {fence} attain {the height of} ten handbreadths.
A fence may also be made of {vertical} canes, providing the space between the canes be less than three handbreadths.

All these regulations apply to a caravan only - these are the words of Rabbi Yehuda.
And the Sages say: They did not speak {only} of a caravan, but they only spoke of a caravan {in the previous Mishna} because that is the common case.

Any partition not constructed warp and woof {that is, of both vertical and horizontal lines} is no partition - these are the words of Rabbi Yossi beRabbi Yehuda.
And the Sages say: any one of the two. {either horizontal or vertical strips}

{Eruvin 17a}
And four things were exempted to {warriors in} a camp: They may bring wood from any place {without respecting the rights of ownership}, and from washing their hands {before eating}, and from demai {food of which it is uncertain that maaser has been taken of it}, and from having to construct an eruv.

{Eruvin 16b}
Gemara:
Rav Nachman lectured in the name of our Rabbenu Shmuel: A courtyard which is used for its empty space {Rashi: for the purpose of that which is outside it - e.g. the watchman stays there to watch what is in the field} and is not fenced in warp and woof, but rather warp and not woof, or woof and not warp - to an individual, we give him bet satayim {an area in which one can grow 2 seah of grain} which is 100 cubits by 50 cubits - Since a bet seah is 50 by 50 cubits, a bet satayim is 100 X 50, which is 70 cubits and change X 70 cubits and change, like the courtyard of the Mishkan, as it is written {Shemot 27:18}:

יח אֹרֶךְ הֶחָצֵר מֵאָה בָאַמָּה וְרֹחַב חֲמִשִּׁים בַּחֲמִשִּׁים, וְקֹמָה חָמֵשׁ אַמּוֹת--שֵׁשׁ מָשְׁזָר; וְאַדְנֵיהֶם, נְחֹשֶׁת.

18 The length of the court shall be a hundred cubits, and the breadth fifty every where, and the height five cubits, of fine twined linen, and their sockets of brass.

and it is called a courtyard, and it was constructed of posts upon which were curtains in the manner of travellers of the deserts, and all matters of Shabbat we learn from the Mishkan, and therefore, an individual we grant a bet satayim, [two, we grant them bet satayim], three is made into a caravan and we give them all they require, and even though it is warp without woof, and so is the halacha.

Rav Gidal cited Rav: Three are permitted in seven and forbidden in five, and Rav Ashi explained this as follows: If they {the three} required six, that is, a bet 6 seah {3 people X 2 seah each = 6 seah}